Similarly, composer Ben Johnston uses a "โ" as an accidental to indicate a note is lowered 21.51 cents, or a "+" to indicate a note is raised 21.51 cents (which is the width of a syntonic comma.[2][3] 498.04 + 21.51 = 519.55 (Just perfect fourth + syntonic comma = F+).
^John Fonville. "Ben Johnston's Extended Just Intonation โ A Guide for Interpreters", p. 109, Perspectives of New Music, vol. 29, no. 2 (Summer 1991), pp. 106โ137